# Mercury Isotope Variability in Pyrenean Lake Sediments during the Late Holocene: Sources, Deposition, and Environmental Controls

## TL;DR

This study uses mercury isotopes in lake sediments to track historical pollution sources and environmental changes over 4000 years in the Pyrenees.

## Contribution

The study introduces a multiarchive and multialtitude approach to distinguish mercury sources and depositional processes in different ecosystems.

## Key findings

- Lake Estanya shows localized mercury signals due to historical land-use changes.
- Lake Marboré reflects regional atmospheric mercury deposition dominated by wet deposition.
- Mercury isotopes in alpine lakes can indicate past climate phases through even-MIF variations.

## Abstract

Atmospheric mercury (Hg) emissions represent a persistent
global
threat to ecosystems and human health. Stable Hg isotopes have emerged
as powerful tools to trace historical pollution sources and reconstruct
depositional pathways in natural archives. In this study, we present
a 4000-year reconstruction of Hg isotopic composition from two Pyrenean
lake sediment records (Lake Marboré and Lake Estanya) located
along an altitudinal gradient and compare them with those of a nearby
ombrotrophic peatland (Estibere mire). Both lakes exhibit a long-term
increase in Hg accumulation rates and shifts in isotope values since
the onset of the Modern Period (∼16th century), consistent
with intensified anthropogenic emissions. However, the isotopic patterns
differ: Lake Estanya, located in a lowland area with historical land-use
changes, reflects a more localized Hg signal, whereas the high-elevation,
remote Lake Marboré preserves a broader regional atmospheric
imprint, dominated by wet deposition. The comparison with Estibere
mirepristine and situated within the same air mass trajectory
as Marboréreveals a consistent offset in Δ199Hg values yet strikingly similar temporal trends, indicating
a shared regional source signal modulated by ecosystem-specific processes.
This multiarchive and multialtitude framework provides a rare opportunity
to disentangle Hg source signatures from depositional and postdepositional
transformations. Moreover, variations in even-MIF (Δ200Hg) in the alpine lake show the potential to reflect past climate
phases, highlighting the additional value of Hg isotopes as paleoclimatic
proxies. Our results underscore the importance of integrating different
ecosystem archives to improve reconstructions of atmospheric Hg dynamics
and to refine interpretations of legacy pollution and climate interactions.